The present invention relates to enhanced oil recovery techniques and, in particular, to an enhanced oil recovery technique wherein an organic vapor phase is injected into an oil-bearing formation.
There are numerous enhanced oil recovery techniques. Exemplary enhanced oil recovery techniques include chemical processes (e.g., surfactant flooding, polymer flooding, and caustic flooding), thermal processes (e.g., steam stimulation or cyclic steam injection, steam or hot water flooding, and in situ combustion), miscible displacement processes (e.g., miscible solvent flooding, carbon dioxide flooding, and inert gas flooding), and foam displacement (e.g., foam displacement variations of steam or hot water flooding, carbon dioxide flooding, and inert gas flooding).
Each enhanced oil recovery process has its advantages, limitations, and/or disadvantages. For example, steam stimulation or cyclic steam injection employs heat to lower the viscosity of the oil in the formation being treated. However, the temperature achievable by the steam is limited by the pressure of the formation. For heavy crude oil-bearing formations, which are generally within 2,000 feet, and more typically within about 1,000 feet of the ground surface, the steam temperature typically attained at the formation depth where the steam is injected is only about 235.degree. C. at a depth of about 1,000 feet and only about 280.degree. C. at a depth of about 2,000 feet. In addition, the steam condenses in the formation, thereby forming water which is immiscible with the oil and which potentially can be a factor in a host of other problems.
Regarding miscible solvent flooding, the solvent is miscible in the oil and does not have the disadvantages associated with the water formed in the steam stimulation process. However, the solvent is a liquid and, therefore, unlike steam, can only contact a much smaller portion of the formation. Furthermore, the miscible solvent flooding process in not a thermal process and does not employ any significant amount of heat to lower the viscosity of the oil present in the formation.